Afferent neural influences from cardiopulmonary pressoreceptors may reflexly alter sympathetic outflow to the kidney thereby influencing renal control of intravascular volume. The influences of cardiopulmonary vagal afferent nerves on renal function have been investigated. However, little is known about the function or synaptic connections of cardiopulmonary afferent nerves traversing sympathetic nerves. Possible influences of these afferent nerves in the kidney have not been studied. Thus, the objective of this research is to define the reflex influence of cardiopulmonary "sympathetic" afferent nerves (CPSAN) on renal sympathetic efferent nerves (RN,. This information will provide a strong basis for determining if renal compensatory responses to intravascular volume change are triggered in part by CPSAN. CPSAN will be activated by electrical stimulation, by intravascular volume expansion or by selective increases in pressure in cardiac chambers or thoracic vasculature in chloralose anesthetized, vagotomized, sino-aortic denervated cats. CPSAN and RN activity will be recorded with standard electrophysiological techniques and evaluated with computer analyses. Renal functions such as sodium excretion and GFR will be monitored. Forebrain and spinal components of CPSAN-RN reflexes will be determined. Correlations between CPSAN and RN discharges will be evaluated during procedures which increase CPSAN activity. Specificity of cardiopulmonary-renal reflexes will be determined by measuring the response of various efferent sympathetic nerves to activation in CPSAN. Effects of CPSAN on renal function will be measured and correlated with changes in RN activity. Evidence will be accumulated which supports or denies the hypothesis that CPSAN contribute to the control of intravascular volume via specific neural influences on the kidney. This hypothesis has been supported by preliminary experiments (Fed. Proc. 35:239, 1976; Neurosci. Abst. 2:93, 1976). Finally, a preliminary investigation of interactions of CPSAN with other afferent influences on RN activity will be initiated. The ultimate goal of this research is to elucidate specific neural influences on the kidney which contribute to the control of intravascular volume.